Among the polyester fibers, those based on polyethlene terephthalate continue to be the most important, although fibers based on 1,4-dimethylenecyclohexane terephthalate have become commercially available. Developments in both homo- and co-polyesters have continued and many modified versions of polyethylene terephthalate have recently appeared on the market. With the advent of new fibers, the search is continued for dyes which build up on the various types of polyester fabric proportionate to the amount of dye applied, and which are characterized by good light and excellent sublimation properties.
Monoazo dyes in which the coupler portion is a 1-aryl-5-pyrazolone have not found wide acceptance as disperse dyes for the coloring of polyester fabric. Previously known dyes of this class do not provide intense enough dyeings to satisfy the needs of the textile trade and the weak dyeings obtained are usually not fast to the action of light or dry heat. Attempts to improve these deficiencies have usually resulted in even lower affinities. The shades, if they could be built up into adequate strength, are of interest because attractive greenish yellow hues can be obtained. Furthermore, such yellows are usually not photochromic as contrasted with the redder yellows which result fom phenolic or aryl amino couplers.
The use of pyrazolone azo dyes on polyester has been previously suggested. Joyce, U.S. Pat. No. 3,019,217, discloses a dye prepared by coupling ortho-chloroaniline into 1-phenyl-3-carbethoxy-5-pyrazolone. Although Joyce reported that his dye provided excellent color value, good crock resistance and excellent light fastness on polyester fibers, Stanley in U.S. Pat. No. 3,212,841 reported that the dye of Joyce is not suited for application by thermofixation methods because of sublimation or volatilization during processing. In Column 5 of the Stanly patent it was noted that the dye of Joyce had poor sublimation fastness and was not suitable for high temperature usage. Stanly reported that his dyes, made with a diazotized alpha -aminoanthraquinone base, showed, when dyed on polyester, an unexpected fastness to sublimation. Stanly, however, recommended application by thermofixation and noted that when carrier dyeings were made at or near boiling for 45 minutes, the dyeings were not as strong or bright as those obtained by the thermofixation method.
According to the present invention, a class of new arylazopyrazolone dyes are provided which have greatly improved affinity over known pyrazolone structures for polyester fibers. The new dyes color polyester fibers in strong, bright greenishyellow hues, a shade of yellow difficult to obtain, especially when it is accompanied by good dyeability and excellent fastness properties. The dyes according to the invention are superior to the azopyrazolones suggested by the prior art for polyester fiber because by using the new dyes useful dyeings of excellent fastness properties, brightness, color value and buildup can be obtained regardless of whether the dyeing is done by carrier, pressure or thermofixation methods. Furthermore, the dyes of the invention are not photochromic.